The present invention relates to an optical information reproducing apparatus and a method of setting a quantity of light in an optical information reproducing apparatus that may be applied to an optical disk apparatus for accessing a phase-change-type optical disk.
In an optical disk apparatus for accessing a phase-change-type optical disk, a drive signal having a high-frequency sine-wave signal superimposed thereon may be applied to drive a laser diode for intermittently energizing the laser diode to reproduce information recorded in the optical disk. As a result, the Signal-to-Noise (xe2x80x9cS/Nxe2x80x9d) ratio of a reproduced signal is effectively prevented from being degraded by the introduction of noise into the laser beam. However, by driving the playback laser diode with such a drive signal, some of the information recorded at an increased recording density in the optical disk may be erased even if the average power is sufficiently lower than the power required to erase data. The erasure of information causes increased jitter upon reproduction. Therefore, this type of optical disk apparatus must operate at optimum conditions, by setting an ideal Direct Current (xe2x80x9cDCxe2x80x9d) signal level of a drive signal and amplitude of a high-frequency sine-wave signal in its designing stage, when applying the laser beam.
If the driving conditions can be selected easily based on the DC signal level of the drive signal and the amplitude of the high-frequency sine-wave signal, then the process of designing the optical disk apparatus may be simplified, and optical disks having different characteristics may be handled appropriately.
Therefore, an object of the present invention is to overcome the above-described problem(s) by providing an optical information reproducing apparatus and a method of setting the quantity of light in an optical information reproducing apparatus for easily and reliably selecting conditions to drive a laser diode with a drive signal having a high-frequency signal superimposed thereon.
Other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and the drawings.
In accordance with an embodiment of the present invention, the power of a playback laser beam may be set such that the peak power of the laser beam except for a relaxation oscillation component does not exceed the power required to erase data recorded in an optical information recording medium. The relaxation oscillation component of the laser beam has a large chromatic dispersion and a small heating effect when focused on optical information recording medium. Consequently, if the power of the laser beam is set such that the peak power of the laser beam except for the relaxation oscillation component does not exceed the power required to erase data recorded in optical information recording medium, then driving conditions can easily and reliably be established.
Thus, in accordance with the invention, conditions for driving a laser diode with a drive signal having a high-frequency signal superimposed thereon may be easily and reliably selected.